Ceramic multilayer electronic components, such as multilayer capacitors and multilayer inductors, and ceramic multilayer substrates are generally manufactured by alternately laminating a plurality of unfired ceramic green sheets of dielectric, magnetic materials or the like and internal conductive paste layers, and co-firing the laminate at a high temperature. Noble metals have been mainly used for the internal conductors, but base metal materials such as nickel, etc. have recently found wide application.
When nickel particles are fired in a non-oxidizing atmosphere such as an inert atmosphere or reducing atmosphere to prevent oxidation, sintering occurs at an early stage, and sintering and shrinkage start at a low temperature of 400° C. or less even when single-crystal particles with a comparatively low activity are used. Meanwhile, sintering of ceramic layers generally starts at a much higher temperature than the above temperature. For example, barium titanate starts sintering at about 1200° C. A problem occurring because of such a difference in shrinkage behavior is that when an internal conductive paste containing a nickel powder and ceramic sheets are co-fired, the ceramic layers do not shrink together with the nickel films, and therefore delamination or cracks can easily occur between the internal conductor layers and ceramic layers.
With one of the suggested methods for solving the aforementioned problem, the sintering initiation temperature of nickel particles is increased, for example, by coating carbon on the nickel particles or incorporating carbon therein (PTL (patent literature) 1 and PTL 2). PTL 1 discloses a metal powder in which a carbon coating film is formed on the nickel powder surface by producing a nickel powder by a vapor phase hydrogen-reduction method, or the like, and then bringing the nickel powder into contact with a hydrocarbon gas at 300° C. to 600° C. PTL 2 discloses a carbon-containing nickel particle powder obtained by heating a dispersion liquid containing nickel particles and a polyol at 150° C. to 350° C. to cause carbon adsorption on the surfaces of nickel particles and/or permeation of carbon into the nickel particles.
Further, surface modification by coating a carbon film on fine metal particles of nickel, or the like, which are used in sensors or magnetic materials, this application being entirely different from that described hereinabove, is also known. For example, PTL 3 and PTL 4 disclose producing nickel particles coated with carbon by cooling a metal vapor, which is generated by melting and vaporizing a metallic raw material, under an atmosphere including a hydrocarbon gas such as methane gas.